#ifndef OPENMM_MONTECARLOANISOTROPICBAROSTAT_H_
#define OPENMM_MONTECARLOANISOTROPICBAROSTAT_H_

/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit.                   *
 * See https://openmm.org/development.                                        *
 *                                                                            *
 * Portions copyright (c) 2010-2025 Stanford University and the Authors.      *
 * Authors: Peter Eastman, Lee-Ping Wang                                      *
 * Contributors:                                                              *
 *                                                                            *
 * Permission is hereby granted, free of charge, to any person obtaining a    *
 * copy of this software and associated documentation files (the "Software"), *
 * to deal in the Software without restriction, including without limitation  *
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 * and/or sell copies of the Software, and to permit persons to whom the      *
 * Software is furnished to do so, subject to the following conditions:       *
 *                                                                            *
 * The above copyright notice and this permission notice shall be included in *
 * all copies or substantial portions of the Software.                        *
 *                                                                            *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
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 * -------------------------------------------------------------------------- */

#include "Force.h"
#include "Vec3.h"
#include <string>
#include "internal/windowsExport.h"

namespace OpenMM {

/**
 * This class uses a Monte Carlo algorithm to adjust the size of the periodic box, simulating the
 * effect of constant pressure.
 *
 * This class is similar to MonteCarloBarostat, but each Monte Carlo move is applied to only one axis
 * of the periodic box (unlike MonteCarloBarostat, which scales the entire box isotropically).  This
 * means that the box may change shape as well as size over the course of the simulation.  It also
 * allows you to specify a different pressure for each axis of the box, or to keep the box size fixed
 * along certain axes while still allowing it to change along others.
 * 
 * This class assumes the simulation is also being run at constant temperature, and requires you
 * to specify the system temperature (since it affects the acceptance probability for Monte Carlo
 * moves).  It does not actually perform temperature regulation, however.  You must use another
 * mechanism along with it to maintain the temperature, such as LangevinIntegrator or AndersenThermostat.
 */

class OPENMM_EXPORT MonteCarloAnisotropicBarostat : public Force {
public:
    /**
     * This is the name of the parameter which stores the current pressure acting on
     * the X-axis (in bar).
     */
    static const std::string& PressureX() {
        static const std::string key = "MonteCarloPressureX";
        return key;
    }
    /**
     * This is the name of the parameter which stores the current pressure acting on
     * the Y-axis (in bar).
     */
    static const std::string& PressureY() {
        static const std::string key = "MonteCarloPressureY";
        return key;
    }
    /**
     * This is the name of the parameter which stores the current pressure acting on
     * the Z-axis (in bar).
     */
    static const std::string& PressureZ() {
        static const std::string key = "MonteCarloPressureZ";
        return key;
    }
    /**
     * This is the name of the parameter which stores the current temperature at which the
     * system is being maintained (in Kelvin)
     */
    static const std::string& Temperature() {
        static const std::string key = "AnisotropicMonteCarloTemperature";
        return key;
    }
    /**
     * Create a MonteCarloAnisotropicBarostat.
     *
     * @param defaultPressure     The default pressure acting on each axis (in bar)
     * @param defaultTemperature  the default temperature at which the system is being maintained (in Kelvin)
     * @param scaleX              whether to allow the X dimension of the periodic box to change size
     * @param scaleY              whether to allow the Y dimension of the periodic box to change size
     * @param scaleZ              whether to allow the Z dimension of the periodic box to change size
     * @param frequency           the frequency at which Monte Carlo pressure changes should be attempted (in time steps)
     */
    MonteCarloAnisotropicBarostat(const Vec3& defaultPressure, double defaultTemperature, bool scaleX = true, bool scaleY = true, bool scaleZ = true, int frequency = 25);
    /**
     * Get the default pressure (in bar).
     *
     * @return the default pressure acting along each axis, measured in bar.
     */
    const Vec3& getDefaultPressure() const {
        return defaultPressure;
    }
    /**
     * Set the default pressure acting on the system.  This will affect any new Contexts you create,
     * but not ones that already exist.
     *
     * @param pressure   the default pressure acting on the system, measured in bar.
     */
    void setDefaultPressure(const Vec3& pressure);
    /**
     * Get whether to allow the X dimension of the periodic box to change size.
     */
    bool getScaleX() const {
      return scaleX;
    }
    /**
     * Get whether to allow the Y dimension of the periodic box to change size.
     */
    bool getScaleY() const {
      return scaleY;
    }
    /**
     * Get whether to allow the Z dimension of the periodic box to change size.
     */
    bool getScaleZ() const {
      return scaleZ;
    }
    /**
     * Get the frequency (in time steps) at which Monte Carlo pressure changes should be attempted.  If this is set to
     * 0, the barostat is disabled.
     */
    int getFrequency() const {
        return frequency;
    }
    /**
     * Set the frequency (in time steps) at which Monte Carlo pressure changes should be attempted.  If this is set to
     * 0, the barostat is disabled.
     */
    void setFrequency(int freq);
    /**
     * Get the default temperature at which the system is being maintained, measured in Kelvin.
     */
    double getDefaultTemperature() const {
        return defaultTemperature;
    }
    /**
     * Set the default temperature at which the system is being maintained.  This will affect any new Contexts you create,
     * but not ones that already exist.
     *
     * @param temp     the system temperature, measured in Kelvin.
     */
    void setDefaultTemperature(double temp);
    /**
     * Get the random number seed.  See setRandomNumberSeed() for details.
     */
    int getRandomNumberSeed() const {
        return randomNumberSeed;
    }
    /**
     * Set the random number seed.  It is guaranteed that if two simulations are run
     * with different random number seeds, the sequence of Monte Carlo steps will be different.  On
     * the other hand, no guarantees are made about the behavior of simulations that use the same seed.
     * In particular, Platforms are permitted to use non-deterministic algorithms which produce different
     * results on successive runs, even if those runs were initialized identically.
     *
     * If seed is set to 0 (which is the default value assigned), a unique seed is chosen when a Context
     * is created from this Force. This is done to ensure that each Context receives unique random seeds
     * without you needing to set them explicitly.
     */
    void setRandomNumberSeed(int seed) {
        randomNumberSeed = seed;
    }
    /**
     * Returns whether or not this force makes use of periodic boundary
     * conditions.
     *
     * @returns true if force uses PBC and false otherwise
     */
    bool usesPeriodicBoundaryConditions() const {
        return false;
    }
    /**
     * Compute the instantaneous pressure along each axis of a system to which this barostat
     * is applied.
     * 
     * The pressure is computed from the molecular virial, using a finite difference to
     * calculate the derivative of potential energy with respect to volume.  For most systems
     * in equilibrium, the time average of the instantaneous pressure should equal the
     * pressure applied by the barostat.  Fluctuations around the average value can be
     * extremely large, however, and it may take a very long simulation to accurately
     * compute the average.
     * 
     * @param context    the Context for which to compute the current pressure
     * @returns a vector containing the pressure along each axis
     */
    Vec3 computeCurrentPressure(Context& context) const;
protected:
    ForceImpl* createImpl() const;
private:
    Vec3 defaultPressure;
    double defaultTemperature;
    bool scaleX, scaleY, scaleZ;
    int frequency, randomNumberSeed;
};

} // namespace OpenMM

#endif /*OPENMM_MONTECARLOANISOTROPICBAROSTAT_H_*/
